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<br />The concentrations of Dioxane have varied between Well Nos. 3, 4, and 5, with Well <br />Nos. 3 and 5 staying below 1 ppb, and Well No. 4 exceeding 1 ppb. The City has not <br />used Well No. 4 since Dioxane levels detected in this well exceeded 1.0 ppb. <br /> <br />Well Nos. 3 and 5 could be blended to reduce the total concentration of Dioxane in Well <br />No. 4 to below 1 ppb at the point of consumption. The long term viability of blending is <br />unknown as Dioxane concentrations may increase to levels that prohibits blending. <br /> <br />The City is currently blending Well Nos. 3 and 5 to keep Dioxane concentrations below 1 <br />ppb. However, Well No. 3 is currently in need of rehabilitation, which would require <br />taking it out of service for a number of months. The City does not currently have a viable <br />means to blend Wells No. 4 and 5 to keep Dioxane below 1 ppb during the rehabilitation <br />of Well No. 3. The City may need to add VFDs to the existing wells in order to control <br />the blending process, provide flexibility in the use of the existing wells, and control the <br />concentration of Dioxane into the system. <br /> <br />Advantages <br /> This option would provide the following advantages: <br /> <br />1. Minimal additional capital costs and operator training <br />2. Can be done immediately <br />3. Addition of variable frequency drives for pumps could provide better blending <br />4. Buys time while longer -term solutions are evaluated and implemented and MCL <br />regulations are further updated <br /> <br />Disadvantages <br />This option would provide the following disadvantages: <br /> <br />1. There is a reasonable likelihood that the Dioxane concentration in the City’s <br />aquifer could increase over time based on historical concentrations and trends (see <br />Table 1 in Section 2.4). As stated previously, the concentrations detected at the <br />TCAAP are as high as approximately 60 ppb and the concentrations detected in <br />the City wells has increased over the short time period the City has been <br />monitoring. <br /> <br />2. If the MDH establishes an MCL for Dioxane at or near 1 ppb, the City will be left <br />without a technology to effectively meet the future regulations. Dioxane is <br />currently classified as an emerging contaminant, meaning not enough information <br />is known on the contaminant and an MCL has not yet been established. It is <br />expected that the EPA will continue to study this contaminant and could set an <br />MCL at some point in the future. Blending the water could be only a short term <br />solution depending on a future MCL that could be established by the EPA. <br /> <br />3. The City currently has Well No. 4 shut down because the Dioxane concentration <br />in this well now exceeds the MDH’s recommended health risk limit . Although it <br />is unknown until additional sampling and laboratory results become available; <br /> <br />1,4-DIOXANE PROJECT <br />FEASIBILITY REPORT <br />CITY OF ST. ANTHONY VILLAGE <br />WSB PROJECT NO. 3183-00 PAGE 5